A lower CD4+ cell count was associated with 40% higher risk of incident Afib after adjustment for traditional risk factors (less than 200 cells/mm3 versus more than 350 cells/mm3, P=0.018), Jonathan Hsu, MD, of the University of California San Francisco, and colleagues found.

A higher viral load came with 70% elevated adjusted risk of developing the arrhythmia (more than 100,000 copies/mL versus less than 500 copies/mL, P=0.002), the group reported online in Journal of the American College of Cardiology.

Afib appears to be one more emerging cardiovascular risk for the aging HIV-infected population, along with heart disease, peripheral vascular disease, and congestive heart failure, they concluded.

"Since the advent of highly active antiretroviral therapy, the natural history of HIV has drastically changed, as HIV mortality, AIDS, and AIDS-related hospitalizations have decreased substantially, leading to increased life expectancy," they wrote.

While the findings were suggestive that HIV infection is a risk factor for Afib, the analysis included no uninfected individuals for comparison.

The mechanism behind this relationship, and whether oral anticoagulation improves outcomes in this population, remain unclear as well, the researchers noted.

Their national sample of 30,533 HIV-infected veterans in the Department of Veterans Affairs HIV Clinical Case Registry from 1996 through 2011 captured patient demographic and clinical information, healthcare utilization, and outcomes.

During a median 6.8 years of follow-up, 2.6% of the cohort developed Afib (641 fibrillation, 139 flutter, 60 both) for an incidence rate of 3.6 events per 1,000 person-years.

Results were similar to those in the main analysis when only looking at fibrillation and excluding atrial flutter.

The risk of incident Afib was 60% elevated with a viral load over 100,000 versus less than 500 copies/mL (P=0.011).

The risk was 30% elevated with a CD4+ cell count less than 200 versus more than 350 cells/mm3, although not statistically significant (P=0.106).

A subanalysis suggested that both higher HIV RNA viral load and low CD4+ cell count were associated with Afib risk in both older and younger patients without an interaction.

Additional adjustment for healthcare contacts in terms of annual outpatient visits followed the same pattern, although controlling for hospitalizations somewhat attenuated the results, "suggesting that the association is potentially mediated by the severity of illness and its attendant inflammatory state."

"It is of note that CD4+ cell count and viral load were similar at baseline in those that did and did not go on to develop atrial fibrillation, suggesting a more direct role of HIV severity in the development of atrial fibrillation," Hsu's group wrote, postulating a role of active HIV replication, possibly through inflammation.

One limitation of the analysis was generalizability to other populations who were poorly represented in the VA registry, such as women and those without access to medical care.

The researchers also cautioned about the possibility of residual confounding, detection bias from more medical care in those with more severe HIV infection, and use of administrative data for Afib diagnoses.